The worker received a radiation dose of at least three times the regulatory limit while shredding filters in July at the lab's hazardous waste management division, the Energy Department said.

Four other technicians were exposed, but not internally. All five returned to work the next day.

The filters were used in rooms where nuclear weapons experiments had been conducted. Tests showed the filters held as much as 500 times the amount of a plutonium derivative called curium-244 allowable for the level of precautions taken by the workers.

There will be no fines because the lab is managed by the University of California, which is exempt from monetary penalties.